look and act in less than stellar ways. But recent studies have shown that it’s not only adolescence itself that throws teens—and their families—into a tailspin. Underlying the exhaustion and the irritability, and adding or aggravating a whole slew of other conditions, is sleep deprivation.

What would teens be like if they weren’t continually sleep deprived? If they could get a good night’s sleep night after night, would there be happier, healthier, more energetic, and better-performing youngsters sitting across from us at the dinner table? All signs point to yes. (OK, they’d still be wearing those enormous baggy pants and the spaghetti-strap tank tops with their bellies showing—unfortunately getting enough rest doesn’t solve teen fashion issues.) In simple terms, lack of sleep and being sleep phase delayed make a challenging time of life much harder to cope with by robbing teens of what their bodies need to refresh, repair, fight off damaging physical and emotional conditions, and grow.

But problems don’t arise just from sleepiness—there’s another side to the sleep deprivation issue. When you’re sleeping less, you have to sustain wakefulness longer, and this puts extra stress on your body, which leads to additional problems. Think of it this way: If you’re getting only six hours of sleep, your body has to stay awake for 18 hours— which is nearly impossible to do at peak functionality. It’s very difficult for a human being to sustain wakefulness for 18 or more hours at a clip.

When does functionality drop off? The critical point of dysfunction appears to be when you hit between 15 and 16 hours of cumulative sleep loss. So if your teen is sleeping only five hours a night, when she should be getting more than nine, after four nights (four hours’ loss per night times four nights) functionality will be at a less than optimal level. And that decreased functionality applies across the board—in school performance, emotional stability, behavior, ability to fight off infection, you name it.